Personal direction finding apparatus

ABSTRACT

A personal direction finding apparatus for determining the direction to be followed in order to reach a predetermined spot which includes a headset provided with two earphones and a circuit for generating a track error signal. The circuit includes a compass supported on the headset for outputting a heading signal corresponding to the heading of the direction of travel, a receiver for a position location and navigation system outputting a signal for the heading to be followed via one output, and a track error computing circuit.

BACKGROUND OF THE INVENTION

The present invention relates to a personal direction-finding apparatusmaking it possible to determine a direction to follow in order to reacha predetermined spot, either in a straight line or by following apredefined path.

To find their way on land, sea or in the air, individuals travellingeither on foot or on board a vehicle usually use traditionaldirection-finding means such as the compass or the satellite navigationsystem also known as GPS. These means require the frequent reading ofthe information delivered in order to correct the drift from the path ortrack error and consequently, during each period of reading, the eyesare no longer available for progressing, observing to noting visuallandmarks. In the case of a pedestrian, reading of the informationfurther requires that the pedestrian holds the direction-findingapparatus in order to place it in front of his eyes.

French Patent FR-A-2 731 521 describes an individual goniometricapparatus comprising a means for picking up the radiation of a source,worn on the user's head, a receiver possibly intervening as demodulator,a circuit for processing the goniometric signal and at least oneearphone connected to the output of the processing circuit.

Document "Patent Abstract of Japan" Vol. 95 No. 003 discloses a vocalnagivation device comprising a sensor of the position or of the angle ofrotation of a pivoting wheel of a vehicle and furnishing auditive dataservo-controlled by this orientation.

U.S. Pat. No. 5,334,987 discloses a control system of an aircraftcomprising a GPS receiver making it possible to determine the positionof the aircraft, and a computer producing a flight plan having thedesired orientation to direct the pilot towards the zone that he mustreach.

U.S. Pat. No. 4,774,515 discloses an attitude indicator comprising aheadset with earphones to furnish an individual with data relative tohis position in space.

BRIEF SUMMARY OF THE INVENTION

An object of the present invention is to provide a personaldirection-finding apparatus which is convenient to use, allowing thewearer to be permanently informed as to the track to be followed withouthis eyes and hands having to intervene.

To that end, this personal direction-finding apparatus for determining adirection to be followed in order to reach a predetermined spot eitherin a straight line or by following a predefined path comprises a headsetprovided with two left and right earphones applied on the ears of theuser of the apparatus, to allow a binaural listening of sound signals, acircuit generating a track error signal which represents the angulardeviation between the direction to be followed and the directioneffectively followed by the user of the apparatus, a generator of alow-frequency electric signal in the spectrum of audible frequencies bythe human ear, and a circuit for processing the binaural sounds whichhas inputs connected to the output of the track error signal generatingcircuit and to the output of the low-frequency signal generator, andhaving two outputs respectively connected to the two earphones, in orderto produce sound signals differentiated for the left and right ears as afunction of the track error signal and to furnish, when the user stopsand/or is moving, a servo-controlled sound signal perceived by the useras seeming to come from a point located in the direction to be followed,characterized in that the track error signal generating circuitcomprises a magnetic compass, borne by the headset, outputting amagnetic heading signal corresponding to the magnetic heading of thedirection followed, a receiver of a position location and navigationsystem outputting a heading signal to be followed and a track errorcomputing circuit having a first input connected to the magnetic compassand a second input connected to the receiver and effecting a subtractionbetween the heading signal to be followed and the magnetic headingsignal in order to deliver the track error signal as result of thedifference, this signal being applied to the output of the track errorsignal generator circuit.

The track error signal generating circuit preferably comprises, inaddition to the magnetic compass, a receiver of a position location andnavigation system, by satellites (GPS system) or ground stations, butthe apparatus may also function, in the event of necessity imposed bythe environment, either with a receiver alone or with the magneticcompass alone.

If the apparatus is used in an environment allowing reception of thesignals coming from satellites or ground stations and the use of themagnetic heading given by the magnetic compass, the apparatus in thatcase furnishes, when the user has stopped or is moving, a sound signalservo-controlled by the orientation of his head and of which the sourceseems to come from the direction of the point having the longitude andlatitude selected in the position location receiver.

If the apparatus is used in an environment not allowing reception of thesignals coming from the satellites or ground stations, for example ifthe user of the apparatus is moving in a subaquatic environment (diver),the navigation of a diver equipped with the apparatus is effected on thedata of the magnetic heading to be followed. This data is selected onthe apparatus and the latter delivers, at stop and during movement ofthe diver, a sound signal servo-controlled by the orientation of hishead and of which the source seems to come from the direction of theheading selected.

In the case of use on the ground, a magnetic compass with two axes,analyzing the terrestrial magnetic field in the horizontal plane issufficient. In the case of subaquatic use, a magnetic compass with threeaxes may allow the apparatus to function whatever the position of thediver.

If the magnetic heading data is not sufficiently reliable because of thepresence of magnetic objects nearby, high voltage lines or the nature ofthe subsoil, the position location receiver may be used alone, taking asinformation the track error which it delivers. In that case, the soundsignal is applied to the earphones only if the speed of displacement ofthe user of the apparatus is sufficient to allow the receiver to makeits calculations and the sound signal is in that case notservo-controlled by the orientation of the head of the user of theapparatus, but solely by his direction of displacement.

The circuit generating the track error signal is advantageously equippedwith a switch allowing the selection of one of the three possibleoperational modes of the apparatus, namely, the basic mode with combinedintervention of the receiver and of the magnetic compass, the mode withthe receiver alone active and the mode with the magnetic compass aloneactive. The selection of the operational mode may be effected manuallyor automatically. In this latter case, the apparatus may comprise adevice for automatic mode switching as a function of the validity of theinformation issuing from the magnetic compass and the receiver. Theapparatus then comprises a means intervening on the sound signal appliedto the earphones in order to inform the user of the apparatus of theautomatic mode change by means of a particular, identifiable soundsignal.

The GPS receiver of the apparatus may be integrated in the headset or itmay be constituted by an external receiver provided with a data output.

The information generally available on the GPS receivers, such asdistance from the point selected, output of corridor and qualities ofthe reception of the satellite, may be used to inform the user of theapparatus by an appropriate signal or sound message.

The geographical coordinates of the rendez-vous or track point may beloaded in the GPS receiver either by the user himself or by aradioelectric data transmission.

The apparatus according to the present invention also makes it possibleto effect homing of a radioelectric emission source of which thedirection was acquired during a brief pulse.

BRIEF DESCRIPTION OF THE DRAWINGS

Various forms of embodiment of the present invention will be describedhereinafter by way of non-limiting examples, with reference to theaccompanying drawings, in which:

FIG. 1 is a block diagram of a personal direction-finding apparatusaccording to the present invention.

FIG. 2 is a block diagram of a variant embodiment of the circuitgenerating the track error signal.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The apparatus according to the invention which is shown in FIG. 1comprises a headset 1 worn on the head of the user of the apparatus andwhich comprises two earphones, left 2g and right 2d, appliedrespectively to the two ears of the user of the apparatus, in order toallow a binaural listening of sound signals. The two earphones 2g, 2dare respectively connected to two outputs of a binaural listeningprocessing circuit 3 with two inputs. To a first input of the processingcircuit 3 there is connected the output of a circuit 4 comprising allthe components located inside a rectangle traced in broken lines. Thiscircuit 4 is intended to produce a track error signal s_(c) whichrepresents the angular deviation C between a direction X having to befollowed by the user to reach a rendez-vous point P and the direction Yeffectively followed by the user. The direction Y followed by the useris characterized by its magnetic heading A, i.e. the angle formed bythis direction Y with the direction N of the magnetic North. Thedirection X to be followed towards the rendez-vous point P ischaracterized by the fixing of the rendez-vous point, i.e. the angle Bformed by the direction X with the direction N of the magnetic North.

The apparatus also comprises a low-frequency electric signal generator 5which is connected to the second input of the binaural listeningprocessing circuit 3. This low-frequency signal generator emits a signalin the spectrum of the frequencies audible by the human ear.

In the binaural listening processing circuit 3, the low-frequency signalof the generator 5 is modified, as a function of the value of the trackerror signal s_(c), so as to produce at the two outputs of theprocessing circuit 3, signals which are differentiated concerning theiramplitude, their phase, and the frequency response, which aretranslated, in the earphones 2g and 2d, by differentiated sound signalsapplied to the right and left ears. The synthesis of the differentiatedsound signals is translated, for the user of the apparatus, by anauditive perception as if the rendez-vous point P constituted the sourceof sound of the signals. The user of the apparatus may therefore bepermanently oriented, whatever the nature of the terrain or theenvironment in which he is moving, towards the rendez-vous point P,thanks to his automatic guiding towards the "fictitious" sound emissionsource P.

The principal elements constituting the circuit 4 generating the trackerror signal will now be described in greater detail. The two principalconstituents of the circuit 4 are a magnetic compass 6 and a receiver 7of a position location and navigation system by satellites or groundstations, referred to hereinafter, for simplification, as GPS receiver.The magnetic compass 6, borne by the headset 1, permanently outputs asignals S_(a) corresponding to the magnetic heading A, i.e. which is afunction of the orientation of the headset 1, therefore of the user'shead. The output of the magnetic compass 6 is connected to a first inputof a track error computing circuit 8. This circuit comprises a secondinput to which is applied a heading signal S_(b) to be followedrepresenting the heading B, i.e. the angle of the direction X with thedirection N of the magnetic North. This signal is furnished either fromthe GPS receiver 7 or from a manual input circuit 9, circuit in whichthe user may himself enter the geographical coordinates of therendezvous point P in order correlatively to deliver a heading signalS_(b) to be followed. The selection of the source of the heading signalS_(b) to be followed is effected by means of a switch 11 connectedbetween the outputs of the GPS receiver 7 and the manual input circuit 9and the second input of the computing circuit 8.

The GPS receiver 7 also delivers, on another of its outputs, the trackerror signal S_(c) which is used when the magnetic heading data is notsufficiently reliable, as will be specified hereinafter. This output maybe connected directly to the first input of the binaural listeningprocessing circuit 3, by means of a second switch 12 which is connectedbetween, on the one hand, the output of the GPS receiver 7 and theoutput of the computing circuit 8 and, on the other hand, the firstinput of the processing circuit 3.

The two switches 11 and 12 are controlled by an operational modeselector 13 which is manually controlled by the user or automatically asa function of the validity of the information issuing from the magneticcompass 6 and from the GPS receiver 7.

If the apparatus is used in an environment allowing the reception of theGPS signals coming from satellites and the use of the magnetic headingA, i.e. if the information issuing from the GPS receiver 7 and from themagnetic compass 6 is valid, the switches 11 and 12 are each placed in afirst position, as shown in solid lines in FIG. 1. In that case, thesecond input of the computing circuit 8 is connected, by switch 11, tothe output of the GPS receiver 7 so as to receive therefrom the headingsignal S_(b) to be followed and its output is connected, by switch 12,to the first input of the processing circuit 3. The computing circuit 8is a circuit for subtraction between the signals S_(b) and S_(a), so asto deliver the track error signal S_(c) as result of their difference.In other words, the circuit 8 effects the calculation S_(c) =S_(b)-S_(a). In this first operational mode which is the basic operationalmode and which is generally used, the apparatus furnishes, when the userhas stopped and when he is moving, a sound signal which isservo-controlled by the orientation of the head and of which the sourceseems to come from the direction of the point P of which the longitudeand latitude are selected in the GPS receiver 7.

If the apparatus is used in an environment not allowing reception of theGPS signals coming from the satellites, for example if the user (diver)is moving in a subaquatic environment, his navigation may be effected onthe data of the heading to be followed, B, entered manually by the userin the circuit 9. In that case, the switch 11 is placed in its secondposition so as to connect the output of the manual input circuit 9 tothe second input of the computing circuit 8. There again, in this secondoperational mode, with the use of the magnetic compass 6 alone, theapparatus delivers, at rest and in the course of displacement, a soundsignal servo-controlled by the orientation of the head and of which thesource seems to come from the direction X of the selected heading B.

If the magnetic heading data A is not sufficiently reliable, theapparatus may be used, in a third operational mode, by using solely theGPS receiver 7. In that case, the switch 12 is placed in its secondposition in which it connects the output of the GPS receiver 7delivering the track error signal S_(c) directly to the first input ofthe processing circuit 3. In that case, the sound signal is not appliedto the earphones 2g, 2d if the speed of displacement of the user is toolow to allow the GPS receiver 7 to effect its calculations and theinformation is not servo-controlled by the orientation of the head butsolely by the direction of displacement of the user.

The circuit 4 generating the track error signal s_(c) comprises severalother functional elements. To the GPS receiver 7 there are connected acircuit 14 allowing manual input, to the GPS receiver 7, of thegeographical coordinates of the track or rendez-vous point P, and aradioelectric receiver 15 allowing a downloading of the geographicalcoordinates of the track point via a radioelectric data transmission.

The circuit 4 may also comprise a control logic circuit 16 with aplurality of inputs and having the output connected to the low-frequencysignal generator 5. A first input 16a of the control logic 16 isconnected to the mode selector 13 so as to provoke, during an automaticchange of operational mode, the emission, by the low-frequency signalgenerator 5, of a signal characterizing the change of mode. A secondinput 16b of the control logic 16 is connected to an output 7a of thereceiver 7 emitting a signal characterizing the present state of the GPSreceiver 7. A third input 16c of the control logic 16 is connected to asecond output 7b of the GPS receiver 7 delivering a signal representingthe distance from the rendezvous point P. The signals applied to theinputs 16b and 16c of the control logic 16 are used to control thelow-frequency signal generator 5 so that the latter emits differenttypes of sounds and/or messages as a function of the states of the GPSreceiver 7, for example depending on whether the user is located in apredetermined corridor or outside of this corridor, and of the distancefrom the rendezvous point P selected.

FIG. 2 shows a variant embodiment making it possible to effect a homingof a point P constituted by a radioelectric emission source periodicallyemitting a brief signal followed by a long period of silence. In thiscase, a radiocompass 17, worn on the user's head, makes it possible todetect, at instant t0, the brief radioelectric signal emitted by thesource P and to determine the direction of the source P with respect tothe orientation of the head, this direction being characterized by thesignal S_(ct0) emitted by the radiocompass 17. Simultaneously, themagnetic compass 6 furnishes an indication of the magnetic heading S_(a)of the orientation of the head Y at instant t0. A computing circuit 18establishes the fixing S_(b1) of the source P at instant t₀, byeffecting the addition S_(bl) =S_(ct0) +S_(a). The output of circuit 18is connected to a memory 19 which stores the value S_(bl). After storingthis initial information, the user may continue to orient towards thesource P, although the latter has ceased its emission. To that end, thesignal S_(b) at the output of the memory 19 is directed by the switch11, in that case placed in a third position, towards the second input ofthe track error computing circuit 8. The circuit 8 then effects thecalculation of the track error S_(c) by the following operation: S_(c)=S_(b) -S_(a). The value of the corresponding track error signal isapplied to the processing circuit 3 to allow the user to continue tohead towards the source P, although the latter is silent.

The personal direction-finding apparatus according to the presentinvention may be used in various ways. For example, the user may wish tobe able to advance in a determined corridor. In that case, the user,after having entered the geographical coordinates of the track point tobe reached by means of the circuit 14 or 15, places the GPS receiver 7in the "corridor" mode. The apparatus itself then makes it possible toadvance in a corridor of defined width, by following the sound guiding.

In the case of advance in a hostile environment, the user's hands andeyes are 100% available to ensure safety of the advance and, in order toconserve the availability of hearing, the "corridor alert" mode of theGPS receiver 7 is triggered off. The sound signals are then applied bythe earphones 2d, 2g only in the event of excessive deviation withrespect to the ideal track.

As has already been indicated, the apparatus also allows the homing of acorrespondent by radioelectric means. The geographical coordinates ofthe correspondent are transmitted radioelectrically, these coordinatesare received in the receiver 15 and automatically loaded in thecorrespondent's GPS receiver in order to allow homing.

The user may also use the apparatus as "Ariadne's clue". To that end, heplaces the GPS receiver 7 in automatic point recordal mode and when heso desires, he can thus return to the starting point with the aid of thesound guiding, by selecting the "return" mode on the GPS receiver 7.

In the case of use by a diver in a subaquatic environment, the diver maymake the precise acquisition of the track to be followed, by means ofthe gps receiver 7, by surfacing, and he can continue his routesubmerged, using only the heading information furnished by the magneticcompass 6.

What is claimed is:
 1. Personal direction-finding apparatus fordetermining a direction to be followed in order to reach a predeterminedspot either in a straight line or by following a predefined path,comprising a headset (1) provided with left (2g) and right (2d)earphones for binaural monitoring of sound signals, a circuit (4)generating a track error signal (S_(c)), representing an angulardeviation (C) between a direction (X) to be followed and a direction (Y)effectively followed by a user of the apparatus, a generator of alow-frequency electric signal (5) in a spectrum of audible frequenciesand a processing circuit (3) having first and second inputs,respectively connected to an output of the track error signal generatingcircuit (4) and to an output of the low-frequency signal generator (5),and having two outputs respectively connected to the two earphones(2g,2d), in order to produce sound signals differentiated for the leftand right earphones as a function of the track error signal (S_(c)) andto furnish a sound signal perceived by the user as seeming to come froma point located in the direction (X) to be followed, wherein the circuit(4) generating the track error signal (S_(c)) comprises a magneticcompass (6), borne by the headset (1), outputting a first magneticheading signal (S_(a)) corresponding to a magnetic heading (A) of thedirection (Y) effectively followed, a receiver of a position locationand navigation system (7) outputting a second heading signal (S_(b)) tobe followed representing a heading of the direction (X) to be followedand a track error computing circuit (8) having a first input connectedto the magnetic compass (6) and a second input connected to the receiver(7) and effecting a subtraction between the second heading signal(S_(b)) to be followed and the first magnetic heading signal (S_(a)) inorder to deliver the track error signal (S_(c)) as a result of thedifference, the track error signal being applied to the output of thetrack error signal generator circuit (4).
 2. Apparatus according toclaim 1, further comprising:a manual input circuit (9) to entergeographical coordinates of a rendezvous point (P) in order to deliverthe second heading signal (S_(b)) to be followed; and a first switch(11) connected between a first output of the receiver (7) and an outputof the manual input circuit (9) and the second input of the track errorcomputing circuit (8) to which the second heading signal (S_(b)) to befollowed is applied.
 3. Apparatus according to claim 2, furthercomprising a second switch (12) connected between a second output of thereceiver (7) directly delivering the track error signal (S_(c)) and anoutput of the track error computing circuit (8) and the first input ofthe processing circuit (3).
 4. Apparatus according to claim 3, whereinthe track error generator circuit (4) generating the route error signal(S_(c)) comprises an operational mode selector (13) controlling thefirst and second switches (11, 12) and which is one of manually andautomatically controlled as a function of validity of informationissuing from the magnetic compass (6) and the receiver (7).
 5. Apparatusaccording to claim 4, wherein the track error generator circuit (4)generating the track error signal comprises a control logic circuit (16)having a plurality of inputs (16a, 16b, 16c) connected to theoperational mode selector (13) and to the receiver (7) and having anoutput connected to the low-frequency signal generator (5) so that thelow-frequency signal generator (5) emits a plurality of characteristicsignals as a function of signals emitted by the receiver (7) and upon achange of operational mode.
 6. Apparatus according to claim 5, whereinthe plurality of inputs of the control logic circuit comprise:a firstinput (16a) connected to the mode selector (13) so as to provoke, uponan automatic change of operational mode, emission, by the low-frequencysignal generator (5), of a signal characterizing the change of mode; asecond input (16b) connected to a third output (7a) of the receiver (7)emitting a signal characterizing a present state of the receiver (7);and a third input (16c) connected to a fourth output (7b) of thereceiver (7) delivering a signal representing a distance from therendezvous point.
 7. Apparatus according to claim 1, wherein there isconnected to the receiver (7) a manual entry circuit (14) allowing amanual entry into the receiver of geographical coordinates of one of aroute and a rendezvous point (P).
 8. Apparatus according to claim 1,wherein there is connected to the receiver (7) a radioelectric receiver(15) to allow download of geographical coordinates of a route point viaa radioelectric data transmission.
 9. Apparatus according to claim 1,wherein homing to a point (P) constituted by a radioelectric emissionsource periodically emitting a signal followed by a period of silence ispossible, wherein the apparatus further comprises:a radiocompass (17)worn on a user's head to detect the signal emitted at a determined timeinstant (t₀) by the radioelectric emission source and to furnish a firstsignal (S_(ct0)) characterizing a direction of the radioelectricemission source with respect to the orientation of the user's head; asecond computing element (18) for establishing a fixing (S_(b1)) of theradioelectric emission source at the determined time instant (t₀) byeffecting the addition of the first signal (S_(ct0)) and the firstmagnetic heading signal (S_(a)) corresponding to the orientation of theuser's head at the determined time instant (t₀); and a memory (19)connected to an output of the second computing element (18) to store thefixing (S_(b1)) of the radioelectric emission source at the determinedtime instant (t₀), an output of the memory (19) being connected to thesecond input of the track error computing circuit (8) which delivers thetrack error signal (S_(c)).
 10. A direction-finding apparatus fordetermining a direction to be followed to reach a predeterminedlocation, the apparatus comprising:a headset having left and rightearphones; a compass outputting a compass heading signal correspondingto a direction being followed; a first device for automaticallyproviding a first heading signal corresponding to a direction that is tobe followed and a derived track error signal corresponding to adifference between the direction that is to be followed and a derivedtrack that is being followed; a second device for providing a manualfirst heading signal; a track error computing circuit having a firstinput connected to said compass and a second input receiving one of thefirst heading signal and the manual first heading signal, said trackerror computing circuit providing a computed track error signalrepresenting a difference between the compass heading signal and one ofthe first heading signal and the manual first heading signal; a signalgenerator for generating audio signals; and a processing circuit havinga first input for receiving the audio signals from said signal generatorand a second input for receiving one of the computed track error signaland the derived track error signal, said processing circuit having twooutputs respectively connected to said left and right earphones so as toprovide to the left and right earphones the audio signals that aredifferentiated as a function of the signal received on said secondinput, the differentiated audio signals providing a sound signal in saidearphones that is perceived as coming from the direction that is to befollowed.